✨ DDSIM version of Estimator primitive

[andresbar98]

Creating a DDSIM version of the second qiskit primitive: The "Estimator". This primitive calculates expectation values of observables with respect to the output state of a QuantumCircuit object.
Code is adapted from the BackendEstimator class from https://qiskit.org/documentation/stubs/qiskit.primitives.BackendEstimator.html, which in turn is a child class of the more general BaseEstimator class https://qiskit.org/documentation/stubs/qiskit.primitives.BaseEstimator.html.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (37a442c) 92.6% compared to head (c21519c) 92.7%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #327     +/-   ##
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+ Coverage   92.6%   92.7%   +0.1%     
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  Files         34      35      +1     
  Lines       2584    2702    +118     
  Branches     348     348             
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+ Hits        2393    2505    +112     
- Misses       191     197      +6     

Flag	Coverage Δ		*Carryforward flag
cpp	94.4% <ø> (ø)		Carriedforward from 37a442c
python	87.9% <95.0%> (+1.3%)	⬆️

*This pull request uses carry forward flags. Click here to find out more.

Files	Coverage Δ
src/mqt/ddsim/qasmsimulator.py	98.9% <100.0%> (ø)
src/mqt/ddsim/primitives/estimator.py	94.9% <94.9%> (ø)

[burgholzer]

I think this is looking good! So let's get it in before Christmas 🎉
I just applied some minor corrections to the docs and merged the latest changes from main in.
Many thanks for this contribution.